Processing of Light and Heavy Distillates

In foregoing sections, we presented only the primary processes for petroleum treatment. It is important to note that all these processes are called primary processes because the petroleum only undergoes physical treatment. This means that chemical changes to the feed do not occur. All the processes we will describe in the sections of this chapter are referred to as secondary processes . This is intended to indicate that chemical changes of the feed occur during these treatments. 

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It is not only the mechanism that is important in the processing of light and heavy distillates. The kinetics of the chemical process is also important. Chemical kinetics deals with the velocity of material conversion by the chemical reactions. 

Although there are minor differences in the HCl—vinyl chloride recovery section from one vinyl chloride producer to another, in general, the quench column effluent is distilled to remove first HCl and then vinyl chloride (see Eig. 2). The vinyl chloride is usually further treated to produce specification product, recovered HCl is sent to the oxychlorination process, and unconverted EDC is purified for removal of light and heavy ends before it is recycled to the cracking furnace. The light and heavy ends are either further processed, disposed of by incineration or other methods, or completely recycled by catalytic oxidation with heat recovery followed by chlorine recovery as EDC (76). 

Chapters 5 and 6 of Part III of the book introduce the reader to the science of crude oil refining. An illustration of the complete process scheme that starts from crude oil all the way to final products is given. In particular, the process route of crude oil from the well to the gas station and indeed the car tank is provided. These chapters also present the techniques and technologies involved in most of the important processes used in modern petroleum refineries for processing light and heavy distillate fractions. Chapter 7 in Part III looks at ecological problems that... 

Let us derive a dynamic model of the process with control structure CS2 included. A rigorous model of the reactor and the two distillation columns would be quite complex and of very high order. Because the dynamics of the liquid-phase reactor are much slower than the dynamics of the separation section in this process, we can develop a simple second-order model by assuming the separation section dynamics are instantaneous. Thus the separation section is always at steady state and is achieving its specified performance, i.e, product and recycle purities are at their setpoints. Given a flowrate F and the composition zA/zB of the reactor effluent stream, the flowrates of the light and heavy recycle streams D, and B-L can be calculated from the algebraic equations... 

Because of the tendency toward nonideal behavior of mixtures, it is generally possible to find some component which when added to a given mixture will increase the difference between the volatilities of the light and heavy key components to be separated. The component or material added to the mixture to be separated is called the solvent. When the solvent added to the mixture is withdrawn from the column, usually in the distillate, as an azeotrope with one or both of the key components, the separation process is called azeotropic distillation. The name azeotropic distillation has also sometimes been given to processes where no azeotrope is formed and the solvent is withdrawn almost exclusively in the distillate. 

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